This invention relates to methods and apparatus for determining an optical distance, such as a distance of an object within a field of view, and more particularly to a method and apparatus for scanning distances within a field of view.
A conventional camera includes an objective lens and a light detector, such as a photographic film, CCD array or other photosensitive device or structure. Light from a viewing environment enters the camera through the objective lens and impinges on the light detector. The portion of the viewing environment for which light enters is the camera""s field of view. Some cameras pass the light to a viewfinder or eyepiece allowing an operator to select a desired field of view from the background environment. To take a picture or record, the light detector captures frames of the background light from the field of view.
Often the field of view is divided into discrete picture elements or pixels. In conventional digital video cameras the light detector records data for each pixel within the field of view for a given video frame. The data includes color, intensity and the pixel coordinates (i.e., x,y coordinates).
Conventional still cameras and video cameras include optics for focusing within the field of view. Thus, an operator can select to focus on a near field object or a far field object. Some cameras even include autofocus devices which automatically adjust the focal length of the objective lens to focus within the field of view.
According to the invention, an apparent distance of one or more points within an optical field of view is determined. For example, an apparent distance is determined for each pixel, or for one or more group of pixels, within a field of view. Such distance is also referred to as a depth of view. One advantage of the invention is that pixel data for an object viewed may be recorded, input to a computer and mapped enabling display of a 3-dimensional model of the object. Another advantage is that an augmented display device or camera device can have variable accommodation.
Incoming light is scanned along a raster pattern to direct light for a select pixel onto a light distance detector. The distance is sampled for each pixel or for a group of pixels. In one embodiment a light distance detector is used. In an alternative embodiment a variabe focus lens is used.
The light distance detector includes a concentric set of ring sensors. The larger the spot of light corresponding to the pixel, the more rings are impinged. For light entering from a far distance, such as from infinity to about 20 feet, the spot will be small. For light coming from closer distances the spot is larger. The diameter of the spot is proportional to the distance at which the light originated (e.g., light source or object from which light was reflected). Each ring corresponds to a distance. The number of rings impinged determines the distance for the pixel being sampled.
The variable focus lens (VFL) is included in the light path. For a given pixel to be sampled, the focal length of the VFL is varied to achieve a small spot size. The distance at which the light originated correlates to the resulting focal length of the VFL.
Although, distance is sampled for each pixel or for a group of pixels, light intensity and color also may be sampled to record a digital image of a field of view, such as for a camera implementation.
The invention will be better understood by reference to the following detailed description taken in conjunction with the accompanying drawings.